Abstract
Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb--Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.
Highlights
The study of event-by-event fluctuations was proposed as a probe of the properties of the hot and dense matter generated in high-energy heavy-ion collisions [1,2,3,4,5,6,7,8,9]
The data used in this analysis were collected with the ALICE detector at the CERN Large Hadron Collider (LHC) [27] during the Pb–Pb run in 2010 and the pp runs in 2010 and 2011
For the results presented as a function of the mean charged-particle density dNch/dη, the mean value Nacc in each centrality bin is associated with the measured value for dNch/dη from [30]
Summary
The study of event-by-event fluctuations was proposed as a probe of the properties of the hot and dense matter generated in high-energy heavy-ion collisions [1,2,3,4,5,6,7,8,9]. The occurrence of a phase transition from the Quark-Gluon Plasma to a Hadron Gas or the existence of a critical point in the phase diagram of strongly interacting matter may go along with critical fluctuations of thermodynamic quantities such as temperature. This could be reflected in dynamical event-by-event fluctuations of the mean transverse momentum pT of final-state charged particles. Fluctuations of pT arise from many kinds of correlations among the pT of the final-state particles, such as resonance decays, jets, or quantum correlations To account for these contributions from conventional mechanisms similar studies can be performed in pp, where such correlations are present. The experimental data are compared to different Monte Carlo (MC) event generators
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